The preparation of nitrosobenzene, which is an important intermediate, is known and can be carried out by various methods. It can be used for the synthesis of antioxidants and stabilizers in the rubber and polymers industry, and in particular for the production of 4-aminodiphenylamine (4-ADPA)."
One method for the preparation of nitrosobenzenes is oxidation of corresponding aromatic amines with suitable oxidizing agents, such as hydrogen peroxide, in the presence of a catalyst and in the presence of a suitable solvent.
The preparation of nitrosobenzenes from aromatic amines by catalytic oxidation with hydrogen peroxide is described, for example, by S. Sakaue, T. Tsubakino, Y. Nishiyama, Y. Ishii. Org. Chem. 1993, 58, 3633; S. Tollari, M. Cuscela, F. Porta, J. Chem. Soc., Chem. Commun. 1993, 1510 and in RU-A 1680689; RU-A 2042661; RU-A 2044724; RU-A 2090542 and by E. B. Mel'nikov, G. A. Suboch, E. Yu Belyaev, Russ. J. Org. Chem. 1995, 31, 160-1642 and Z. Zhu, J. H. Espensen, J. Org. Chem. 1995, 60, 1326-1332.
Disadvantages of the processes mentioned are, for example, the use of high-risk solvents, such as chloroform, in amounts which are not practicable on a large industrial scale in order to achieve good yields, the use of toxic compounds, such as hexamethylphosphoric acid triamide, in the preparation of the catalyst, the use of additional co-catalysts and the use of relatively large amounts of catalyst, as well as the use of expensive catalysts. Because of the disadvantages mentioned, a process operated on a large industrial scale would be uneconomical, associated with extensive safety measures.
It has now been found that nitrosobenzenes can be prepared from aromatic amines by catalytic oxidation with hydrogen peroxides in an industrially simple manner and avoiding the disadvantages described above if the oxidation is carried out without the addition of solvent.